The skin insulates and protects the entire body from mechanical, chemical and thermal damage. Beneath the dermis is the subcutaneous tissue which contains many fat cells. The subcutaneous tissue serves as a "shock absorber" and insulates the deeper tissues from extreme temperature changes. The subcutaneous tissue is also responsible for the outer appearance of the body surface. Another major function of the fat cells is to accumulate fat, as a means for storing food. However, for cosmetic or aesthetic reasons, it may be desirable to reduce the volume of fatty tissue in the body. Exercise and diet can sometimes reduce accumulation of fat in the fat cells, but they cannot reduce the number of fat cells or their distribution. The number of fat cells in the subcutaneous tissue is relatively constant. Furthermore, fat accumulation persists despite diet or exercise for many people.
Liposuction is a surgical procedure that permanently removes localized deposits of fat cells, thereby producing a desirable shape of the body or the face through sculpturing. In a typical liposuction, a catheter connected to a high vacuum device is introduced into the fatty tissue through an incision in the skin, and the fat is removed by aspiration. This procedure requires general anesthesia, involves significant blood loss, and has relatively high morbidity and mortality. This problem has been resolved to some extent with the more recent tumescent liposuction. In tumescent liposuction, large volumes of dilute lidocaine and epinephrine are infiltrated into the subcutaneous fatty tissue before the suction stage. Lidocaine and epinephrine are delivered through a canulated hollow tube inserted through a small skin incision into the fatty tissue between the skin and the muscle. Lidocaine is a local anesthetic, and epinephrine causes lipolysis and vasoconstriction. Lipolysis is destruction of fatty structures. Following the infiltration of the mixture of lidocaine and epinephrine, a catheter connected to a high vacuum device is introduced to the fatty tissue and moved rapidly through the tissue to break up the fat cells that are aspired through the catheter. This procedure has significantly less morbidity and has no reported mortality.
During the aspiration part of the liposuction procedure, the surgeon tries to remove the fatty tissue in such a way that a desired sculpted tissue structure is achieved. During this step, it is important not only to remove the fat from the various areas to obtain the desired shape, but also to create a final tissue appearance of the skin that is regular and smooth. Creating a smooth final tissue appearance, however, is not an easy task. The sculpting of the tissue and the final aesthetic appearance of the body are strongly dependent on the technical skill of the surgeon.
Cryosurgery is a procedure for destroying tissue. In cryosurgery, undesirable tissues are frozen and destroyed. The technique is minimally invasive, usually requiring an insertion of only one or more thin, cylindrical, cryosurgical probes into the undesirable tissue. The probes are cooled internally with a cryogen and are insulated except at the tip. The uninsulated tip is inserted in a tumor or other undesirable tissue, and the tissue is frozen from the probe surface outward. When the desired amount of tissue has been frozen, cryogen is prevented from flowing to the probe, and the tissue is allowed to thaw. After cryosurgery, the frozen tissue is left in situ to be reabsorbed by the immune system over time. Since freezing originates from small uninsulated tip of a probe, the procedure can be confined to a region of the diseased tissue, thereby sparing surrounding healthy tissue. The freezing process can be precise and controlled, as the freezing interface is sharp and propagates slowly (in the order of mm/min). A small probe having a diameter of around 3 mm can produce a 3.5 cm ice ball, and therefore treat a relatively large tissue region. When the shape of the pathological tissue is large and complex, several probes can be used simultaneously to generate a frozen region of a desired shape. For example, prostate and liver cryosurgery is currently performed with five 3 mm diameter probes. Multiple sites can be treated separately or together. Because the only physical invasion of the tissue is the insertion of the cryoprobes, cryosurgery does not create a lot of complications and patient morbidity is low. Cryosurgery can produce excellent medical results with less distress and disfiguration at a lower cost. In addition, cryosurgery is not dose limited, therefore retreatment is possible.
Until recently, a major impediment to the extensive use of cryosurgery on internal tissues has been the inability to observe the frozen region deep inside the body, which could cause complications of over or under freezing. Breakthroughs in non-invasive imaging technology, however, have made possible major advances in cryosurgery in general and prostate and liver cryosurgery in particular. Intraoperative ultrasound can image the progress of freezing during cryosurgery by virtue of the fact that the interface between frozen tissue and non-frozen tissue is associated with a change in acoustic impedance that reflects ultrasound waves. Cryosurgery is now almost universally carried out under ultrasound guidance. Another recent improvement in imaging technology for use with cryosurgery is magnetic resonance imaging (MRI). This technique, which images the process of freezing in three dimensions, can monitor the freezing interface with a resolution of 200 gm, and can control its shape through MRI feedback. Additional methods of imaging are being continuously developed. One such method under development is the use of light to image freezing. Cryosurgery can be performed with greater accuracy and control with the assistance of the imaging techniques. Therefore, cryosurgery is gaining acceptance as a first-line therapy for prostate, liver and other cancer therapy.
Mazur's two factor theory explains destruction of tissue by freezing. Much of the research on the effects of freezing on biological materials has focused on the use of freezing for preservation of cells (such as red blood cells, embryos, sperm). This work has shown that an important thermal variable is the cooling rate (change in temperature per unit time) during freezing. The correlation between cell survival and cooling rate is an "inverse U" shape. Cell survival is greatest for the cooling rate at the peak of the inverse "U", and destruction increases above or below this optimal cooling rate for survival. However, different types of cells have different optimal cooling rates for survival. This difference is associated with the structure and mass transfer properties of the cell membrane and the size of the cells. These general findings are incorporated in Mazur's "two factor" theory, which explains how cooling rates relate to cellular damage.
Mazur proposed that since the probability for an ice crystal to form at any temperature is a function of volume during freezing of cells in a cellular suspension, ice will form first in the much larger extracellular space, before each individual cell freezes. Since ice does not incorporate solutes, the ice that forms in the extracellular space will reject the solutes into the remaining unfrozen solution. The concentration of solutes in the extracellular solution will consequently increase. The small volume of intracellular solution results in a correspondingly low probability for ice nucleation to occur inside the cell. Therefore, with sufficiently low cooling rates, the intracellular solution can remain supercooled and unfrozen, when the extracellular solution begins to freeze and exclude solutes. Under these circumstances, the unfrozen cells will be surrounded by a hypertonic solution. To equilibrate the difference in chemical potential between the intracellular and the extracellular solution, water will pass through the cell membrane, which is permeable to water but impermeable to ions and other organic solutes. Therefore, as the temperature of the solution is lowered and additional ice forms in the extracellular solution, water will leave the cell to equilibrate the intracellular and the extracellular concentration, and the cell will dehydrate and shrink. The intracellular solution will remain unfrozen and become hypertonic, causing chemical damage involving denaturation of intracellular proteins. Since chemical damage is a function of time and temperature, the damage will increase with lower cooling rates. Because water transport is a rate dependent process, faster freezing with higher cooling rates decreases the amount of time a cell is exposed to the chemically damaging conditions and increases survival. This explains the increase in cell viability with an increase in cooling rate toward an optimum. However, increasing the cooling rate also results in a more rapid decrease in temperature. The unfrozen water in cells will therefore experience a greater thermodynamic supercooling. The supercooled intracellular solution is thermodynamically unstable, and after reaching a certain value it will nucleate and freeze. It is thought that the intracellular ice formation damages cells. The probability for intracellular ice formation increases with increasing cooling rate, and consequently the survival of frozen cells decreases with increasing cooling rate.
These two modes of damage, chemical at low cooling rates and intracellular ice formation at high cooling rates, form the basis of the "two factor" theory of cellular damage proposed by Mazur. Survival of cells is optimal during freezing with thermal conditions in which these two conflicting modes of damage are minimized.
An object of this invention is to develop a method, and the related apparatus to further reduce the morbidity associated with liposuction and to facilitate greater control over the appearance of the body surface after liposuction. The invention combines cryosurgery with liposuction.